Such corrosion-inhibiting compositions are already widely known and the most efficient of them usually comprise one or more sulfur derivatives, chosen especially from mercapto alcohols and mercapto acids. Thus, patent applications WO 1998/041673, WO 2013/034846 and WO 2013/038100 describe corrosion-inhibiting compositions in which the addition of sulfur derivatives, for example thioglycolic acid, makes it possible to increase the performance of said inhibiting compositions.
However, it has been observed that corrosion-inhibiting compositions comprising one or more sulfur derivatives, such as those defined above, and in particular thioglycolic acid, are sparingly stable on storage, and have a tendency to develop undesired nauseating odors.
These nauseating odors are probably due to the decomposition of the sulfur compounds, and, without being bound by theory, it is now thought that the sulfur derivatives probably partly decompose into hydrogen sulfide (H2S) at the storage temperature. The higher the storage temperature, the greater the decomposition of the sulfur derivatives, and in particular when thioglycolic acid is concerned. This decomposition phenomenon thus makes these corrosion-inhibiting compositions sparingly usable on account of the unpleasant odors given off, which may even be hazardous to users. Specifically, hydrogen sulfide is toxic, even at very low concentrations in air.
The gas and oil industry already uses certain compounds known as H2S scavengers, where they are mainly used by injection into gas, crude oil or water or aqueous fluid pipelines, in order to scavenge (trap, or neutralize) the acidic species present in said pipelines.
These acidic species are mainly due to the presence of moisture and of “acidic” gases, for instance hydrogen sulfide (H2S) and carbon dioxide (CO2) in the presence of H2S.
In this field, it is now commonly established to classify H2S scavengers in two major families, regenerative scavengers and non-regenerative scavengers.
Among the regenerative H2S scavengers, examples that may be mentioned include alkanolamines such as monoethanolamine, diethanolamine or methylethanolamine.
Among the non-regenerative H2S scavengers, examples that may be mentioned include triazines and derivatives thereof, oxidizing agents such as chlorine dioxide, hypochlorites (for example bleach), hydrogen peroxide, transition metal salts (such as iron, cobalt, nickel, chromium, copper, zinc or manganese salts, and the like), or aldehydes, such as formaldehyde and glyoxal.
It might thus be envisaged to use such H2S scavengers for trapping sulfides resulting from the decomposition of the sulfur derivatives present in corrosion-inhibiting compositions. However, the majority of the regenerative scavengers and non-regenerative scavengers suffer from numerous drawbacks that make them unsuitable for use in corrosion-inhibiting compositions.
Thus, amine derivatives, and in particular alkanolamines, are not efficient enough to remove H2S derived from the degradation of thioglycolic acid. Oxidizing agents, such as chlorine dioxide, bleach or hydrogen peroxide are difficult to use on account of their corrosiveness, which goes against the desired aim. In addition, the formation of insoluble solids with some of these H2S scavengers and thioglycolic acid in anticorrosion formulations makes these formulations unsuitable for use, since any risk of blocking and clogging of the injection tubes and pipes must be avoided at all costs. Moreover, aldehydes, such as formaldehyde and glyoxal, are toxic and it is sought to minimize or even to avoid their use.